What is a Sequence?

A sequence is an ordered list of numbers. Each number in the sequence is called a term. You can write a sequence like $a_1, a_2, a_3, ..., a_n$.

For example, $2, 4, 6, 8, 10$ is a sequence of even numbers. The first term $a_1 = 2$, the second term $a_2 = 4$, and so on.

Sequences appear everywhere in programming: array indices, loop iterations, fibonacci numbers, powers of two. Recognizing the pattern lets you predict future terms or compute sums.